Peripherally hydrogenation

The species at the centre of tire rings is usually Si or Ge and tire bridging atom is oxygen. In one study tire peripheral hydrogens on tire phtlialocyanine molecules were replaced by alkyl groups and tire resulting polymers could be rendered soluble in ordinary organic solvents [108, 109 and 110]. Successful deposition of several of tliese materials has been achieved and different techniques were employed to study tlieir stmctural properties [109, ill, ill, ill and 1141. 

Therefore the CH2 groups in cyclodecane are stereochemically non equivalent. There are CH2 groups in which both the hydrogen atoms are peripheral, there are those in which one hydrogen is peripheral and the other is intraannular. The last two types differ from each other in that in one case the peripheral hydrogen is equatorial and in other axial. 

The structural formula for propane shows 3 axial carbon atoms and 8 peripheral hydrogen atoms. The composition of propane can be more compactly expressed as C3 Hg. This representation is a molecular formula. Such a formula does not directly tell how the various atoms are interbonded. 

However, the ESR spectra for coronene monoanion did not exhibit such complicated peaks as corannulene monoanion. This suggests that AE in the coronene ion is smaller than that of the corannulene ion. In fact, the calculated energy barrier AE of one of the Dlh saddle points between the stable Clh structures is 0.2 meV, which is smaller than that of corannulene as mentioned previously. Therefore, the pseudorotation about the D6h JT crossing makes the HFC constant averaged and all the peripheral hydrogen atoms equivalent even at low temperatures. 

Dramatic deviation from planarity may be induced upon replacing the peripheral hydrogens of an oth-... 

The results showed that the hydrogen atoms in the center of the metal-free phthalocyanine molecule (hydrogen in NH bonds) can be exchanged with those in acetylene. It was also suggested that peripheral hydrogen atoms also participate in the exchange reaction. 

The electronic structure seems to play a less important role, as may be speculated on the basis of similar values of NMR chemical shifts of peripheral hydrogen atoms, or by considering analogies in the pattern of the electronic spectra. In order to elucidate in more detail the role of electronic structure in tautomerism, we are now studying porphyrins in which peripheral substitution leads to inner cavity parameters similar to those of porphycenes. 

The use of coordination compounds with peripheral hydrogen-bonding substituents in the formation of infinite one-, two-, and three-dimensional frameworks, which can be used for host/guest chemistry, has recently been reviewed by Beatty. Brammer and Rivas, on the other hand, have reviewed the hydrogen bonding in substituted ammonium salts of the tetracarbonylcobaltate(i) anion. The reader is addressed to these two papers for a detailed analysis. 

Fig. 4.10. Schematic side and top view of the electron cloud in a small molecule electron-rich organic semiconductor (e.g. an ohgothophene or an acene). Because hydrogen is more electronegative than carbon the peripheral hydrogens attract the pi electrons leading to a herringbone stacking. The higher permittivity of neighboring standing molecules leads to the nearly vertical orientation for the first few deposited layers.

The other type of interaction, a ti-ti interaction, is found in crystals of PAHs these are rich in delocalized electrons and mainly consist of sp carbon atoms with peripheral hydrogen atoms attached. Their structures resemble that of graphite in which planar hexagonally disposed layers of carbon atoms are separated by about 4 A. Large PAHs also form molecular complexes with other flat... 

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